A SolidWorks drawing has several colour options that can be customized. Most of these can be located under Tools > Options > System Options tab > Colors. There are the standard listings for “Drawings” that includes things like the Paper Color, Visible Model Edges, and Tangent Edges.
But there are a few other ones that you may not have realize. If you import dimensions from the model using “Model Items”, these will be black. If you manually add dimensions using the Dimension tools, by default these will be grey. This setting comes from the colour settings for “Dimensions, Non Imported (Driven)”.
The title block border and lines by default are a grey colour. This is due to the fact that the lines are generic sketch entities with no colours assigned. As the lines are inside the Sheet Format, they are no longer active. Therefore the colour is picked up by the System Colour setting for “Inactive Entities”. However if you assign a layer colour or line colour to these lines, it will override the inactive System Colour.
Here is a video showing these options along with how layer colours and line colours override the System Options.